Zoom lenses in general require lens groups which move mechanically along the optical axis in order to vary from short to long focal length, which is equivalent to vary from wide-angle lens mode to tele-lens mode. The ratio between longest and shortest focal length is called zoom ratio. The zoom actuators for the mechanical movement are bulky and therefore difficult to integrate into small cameras such as mobile phone (smartphone) or tablet cameras. Also the mechanical tolerances of the actuators may be too large compared to the small dimension of lenses in smartphone cameras. Moreover the mechanical movement of the zoom actuator is relatively slow, in particular when taking snapshots.
Other approaches realize wide-angle- and tele-mode by using dual cameras, having one wide-angle camera and one tele camera side by side. This approach has the disadvantage of a baseline between the optical axes of wide- and tele-lens, which causes parallax errors between the views of both cameras.
Regardless whether using the dual camera or the zoom actuator approach, in any case the overall length of the tele lens is quite long because of the inherently long focal length of the tele lens.
Although there exist techniques for digital cameras with zoom capabilities, it is generally desirable to provide digital cameras with improved zoom capabilities.